It is quite hard to understand your question, as your english is not very clear, but I think you are trying to ask if the `block.blockhash(uint block_number)` can be changed by miners.

The answer is: Yes! The block hash is only known when the block is mined. (This is also the reason you cannot access the block hash of the current block, because it is not known yet.) The block hash depends on (amongst other things) what transactions are in the block and what the successful nonce is that allowed the miner to mine the block.

So while it is not really possible to predict the block hash, it is possible for miners to influence it (such as _not_ broadcast a mined block when the block hash is undesireable for some reason), and therefore I believe it should not be used as a secure source of randomness.